Method for making a plastic drip chamber



A ril 14, 1964 T. H. GEWECKE METHOD FOR MAKING A PLASTIC DRIP CHAMBEROriginal Filed May 19. 1958 FIGZ FIG. 5

INVENTOR.

United States Patent 3 Claims. c1. 1836) This invention relates to dripchambers for the administration of parenteral solutions and made fromtransparent thermoplastic tubing, large diameter tubing being used forthe body of the chamber and small diameter tubing being used for theinlet and outlet. In such chambers it is essential that the inlet tubeproject centrally into the body of the chamber in position so that thedrops may be counted. This is accomplished by flowing the upper end ofthe outer tube inwardly under heat and pressure to a dome shape andfusing it edgewise to the inlet tube at a point intermediate the upperand lower ends. The dome shape is ideal for centering the inlet tube andfor holding the outer tube in a true circular shape. Accordingly eventhough the dome shaped section has thin walls, the inlet tube issecurely held in a central position where the drops can be readilyobserved. The fact that the body of the chamber is circular minimizesdistortion and permits the drops to be accurately counted from any pointof observation. Although the drip chamber looks as though it could bemade only by a molding operation, it is, in fact, made from lengths ofthermoplastic tubing which have a much lower cost. In addition, apolyvinyl plastic drip chamber made by this method may be steril ized ata temperature of 250 degrees F. without distortion whereas a plasticdrip chamber made from the same material by molding would be distortedif exposed to the same conditions for sterilization.

This application is a division of application Serial Number 736,304,filed May 19, 1958 and now abandoned.

In the drawing, FIG. 1 is an elevation of a plastic drip chamber; FIG. 2is a section through the mold for making the drip chamber from lengthsof thermoplastic tubing; and FIG. 3 is an enlarged section through theupper end of the drip chamber.

The liquid to be administered is fed through an inlet tube 1 having itslower end 2 depending centrally within a drip chamber 3. At the upperend of the drip chamber is a dome shaped section 4 which forms theconnection between the body of the drip chamber and the inlet tube 1.The body of the drip chamber and the inlet tube are made ofthermoplastic material such as, for example, one of the vinyl plastics,the body of the chamber being of clear or transparent plastic and theinlet tube being ordinarily colored so that its lower end will bereadily visible through the wall of the drip chamber. At the lower endthe drip chamber is sealed to plastic outlet tubing 5 in anyconventional manner, for example by heat sealing at 6 Although the dripchamber looks as though it could only be made by integrally molding thebody and inlet tube, it is, in fact, made from lengths of standardthermoplastic tubing in a mold such as shown in FIG. 2. The body 7 ofthe mold has at its center an upstanding spindle 8. Surrounding thespindle 8 and in spaced relation thereto is an annular sleeve 10 ofinsulating material slidably received in a bore 11 in the mold body andresiliently urged upward by a coil spring 12. The sleeve 10 is shown inits uppermost position. Between the inner surface of the sleeve 16 andthe outer surface of the spindle 8 is an annular recess 13 slidablyreceiving a length of thermoplastic tubing 14. The lower end of thetubing rests on a shoulder 15 and although the tubing may be quite limp,it is adequately supported throughout its length by the spindle 8 andsleeve 10. When loaded, the upper end of the tube 14 is slightly abovethe spherical or domed surface 16 on the upper end of the spindle 8. Atthe center of the spindle 8 is fixed a small diameter pin 17 whichprojects within a cylindrical cavity 18 in the spindle 8 and provides anannular recess 19 for receiving the lower end of a length of smalldiameter thermoplastic tubing 20. The tubing 20 has a sliding fit in theannular recess 19 and is firmly supported by the pin 17 on its innersurface and by the outer walls of the recess 19 engaging its outersurface.

The mold cap 21 has a rim 22 of insulating material with a tapered mouth23 leading to a dome shaped cavity 24. The taper at 23 on the rimmatches a taper 25 at the upper end of the sleeve 14 providing a tightjoint when the cap is lowered onto the mold body. In the top of the capis an opening 26 through which the tube 20 readily slides as the cap islowered. The mold cap and body are insulated from each other and areconnected to a source 27 of high frequency current which causeslocalized heating of the plastic between the dome shaped surfaces 16 and24 and between the pin 17 and the opening 26 as the mold cap is closedon the mold body.

As the mold cap 21 is lowered, the upper end of the tubing 14 is guidedinto the cavity 24 by the tapered mouth 23 and is bent edgewise inwardtoward the outer surface of the tube 20. The space between the domeshaped surfaces 16 and 24 in the closed position of the mold ispreferably less than the wall thickness of the tubing 14 so that thereis a plastic flow which smooths out any wrinkles and squeezes the fluidplastic into intimate contact with the outer surface of the tubing 20which likewise is in a softened condition by reason of the highfrequency dielectric heating. An examination of the finished productshows that there is produced a dome shaped section 4 having its inneredge fused as indicated at 28 to the outer surface of the tube 1. Insection, the fusion is quite evident due to the difference in colorbetween the plastic. In some cases there may be a skin of liquid plasticfrom the tube 14 flowing up along the outside of the tube 1 and fusedthereto to extend the joint. This is not necessary as adequate sealingis obtained by the edgewise fusion illustrated in FIG. 3. The domesection 4 is free of wrinkles indicating that the plastic is heated to aflowable state so that it can conform to the dome shaped cavity betweenthe surfaces 16 and 24. Because of the flowing of the plastic, it isunnecessary to have slits or notches or the special formations in theupper end of the tube 14 in order to facilitate the inward folding orbending of the material. The ordinary cut end of the tubing is all thatis needed. The closing of the mold by engagement of the tapers 23, 25while the dome surfaces 16, 24 are still quite widely separated provideslateral support for the upper end of the tubing 14 at the start of thebending or forming operation when there perhaps would be a greatertendency for the tube to buckle. As the mold continues its closingmovement, the surfaces 23, 25 re main in engagement and the insulatingsleeve 10 is merely moved downward to the extent necessary to permitcomplete closing of the mold cavity. The dielectric heating produced bythe high frequency current source 27 is confined primarily to theplastic tubing and accordingly acts very rapidly because of the smallmass of plastic to be heated. The complete forming and sealing operationrequires only a few seconds after the lengths of tubing are loaded intothe mold. The tight seal between the tapered surfaces 23, 25 minimizesthe squeezing of plastic out between those surfaces to form an externalridge.

It is not necessary that the tube 1 be joined to the dome section 4intermediate its ends as shown in FIG. 1. If

the annular recess 19 is eliminated so that the lower end of the tube26) is flush with the dome surface 16, the domed section 4 of plasticwill be fused to the lower end of the tube 20 with the same character ofjoints as that illustrated in FIG. 3. There is an actual liquid flow ofthe plastic with the two kinds of plastic coming together.

What is claimed as new is:

1. A mold for making a drip chamber from thermo plastic tubingcomprising a mold body having a cylindrical cavity of insulatingmaterial with an upstanding metal spindle at its center forming anannular recess between it and the cavity for receiving the lower end ofa length of transparent thermoplastic tubing, said spindle having a domeshaped upper end extending above said annular recess and opposite theupper end of said length of tubing, a small diameter metal spindleprojecting up from the center of said dome shaped upper end forreceiving a length of smaller diameter thermoplastic tubing, said domeshaped section having a reentrant annular recess for receiving the lowerend of the smaller diameter tubing a controlled distance below the outersurface of said dome section, a metal mold cap having a cavitycomplementary to and of slightly larger size than said dome section andhaving a central opening slidably receiving the upper end of said smalldiameter tubing, insulating means between said mold cap and body, asource of high he quency voltage connected between the cap and body asthey are closed under pressure together for creating an electric fieldbetween the cap and spindles for softening the tubing and causing theouter tubing to soften and flow to a dome shape and to be fused edgewiseto said small diameter tubing.

2. A mold for making a chamber from thermoplastic tubing comprising amold body having a cylindrical cavity of insulating material with anupstanding metal spindle at its center forming an annular recess betweenit and the cavity for receiving the lower end of a length ofthermoplastic tubing, said spindle having a dome shaped upper endextending above said annular recess and opposite the upper end of saidlength of tubing, a small diameter metal spindle projecting up from thecenter of said dome shaped upper end for receiving a length of smallerdiameter thermoplastic tubing, a metal mold cap having a cavitycomplementary to and of slightly larger size than said dome section andhaving a central opening slidably receiving the upper end of said smalldiameter tubing, insulating means between said mold cap and body, asource of high frequency voltage connected between the cap and body asthey are closed under pressure for creating an electric field betweenthe cap and spindles for softening the tubing and causing the outertubing to soften and flow to a dome shape and to be fused edgewise tosaid small diameter tubing.

3. A mold for making a chamber from thermoplastic tubing comprising amold body having a cylindrical cavity with an upstanding metal spindleat its center, a sleeve of insulating material slidably received in thecavity with its inner surface spaced from the spindle to provide anannular recess between it and the spindle for receiving the lower end ofa length of thermoplastic tubing, said spindle having a dome shapedupper end extending above said annular recess and opposite the upper endof said length of tubing, a small diameter metal spindle project ing upfrom the center of said dome shaped upper end for receiving a length ofsmaller diameter thermoplastic tubing, a metal mold cap having a cavitycomplementary to and of slightly larger size than said dome section andhaving a central opening slidably receiving the upper end of said smalldiameter tubing, spring means urging said sleeve to a position in whichits upper end projects above said mold body in position to be engaged bythe mold cap and forced downward as the cap is closed on the body, saidsleeve supporting said tube as the cap is closed, a source of highfrequency voltage connected between the cap and body as they are closedunder pressure for creating an electric field between the cap andspindles for softening the tubing and causing the outer tubing to softenand flow to a dome shape and to be fused edgewise to said small diametertubing.

167,455 Austria Jan. 10, 1951

1. A MOLD FOR MAKING A DRIP CHAMBER FROM THERMOPLASTIC TUBING COMPRISINGA MOLD BODY HAVING A CYLINDRICAL CAVITY OF INSULATING MATERIAL WITH ANUPSTANDING METAL SPINDLE AT ITS CENTER FORMING AN ANNULAR RECESS BETWEENIT AND THE CAVITY FOR RECEIVING THE LOWER END OF A LENGTH OF TRANSPARENTTHERMOPLASTIC TUBING, SAID SPINDLE HAVING A DOME SHAPED UPPER ENDEXTENDING ABOVE SAID ANNULAR RECESS AND OPPOSITE THE UPPER END OF SAIDLENGTH OF TUBING, A SMALL DIAMETER METAL SPINDLE PROJECTING UP FROM THECENTER OF SAID DOME SHAPED UPPER END FOR RECEIVING A LENGTH OF SMALLERDIAMETER THERMOPLASTIC TUBING, SAID DOME SHAPED SECTION HAVING AREENTRANT ANNULAR RECESS FOR RECEIVING THE LOWER END OF THE SMALLERDIAMETER TUBING A CONTROLLED DISTANCE BELOW THE OUTER SURFACE OF SAIDDOME SECTION, A METAL MOLD CAP HAVING ACAVITY COMPLEMENTARY TO AND OFSLIGHTLY LARGER SIZE THAN SAID DOME SECTION AND HAVING A CENTRAL OPENINGSLIDABLY RECEIVING THE UPPER END OF SAID SMALL DIAMETER TUBING,INSULATING MEANS BETWEEN SAID MOLD CAP AND BODY, A SOURCE OF HIGH FRE-